it was promised during release of TimeTracker 4 (in November 2017), that API for CRUD operations will be released shortly. Do you have any specific date, when we should expect it? We plan to use it for pairing with HR system for registering absences.

In a response to my recent support question about this on Jan 8, 2017, Leah Copeland said "I spoke to our development lead and they are estimating it will be implemented in about two months." (Not to put her on the spot--I'm sure it was intended with the usual development/business schedule caveats, so take it with a grain of salt.)

In a mean time - to set User and ActivityType for WorkLog you have to pass "userId" and "activityTypeId" guids respectively to POST or PATCH request. To find userId or activityTypeId you can execute GET requests "/api/rest/users" and "/api/rest/activityTypes"

Unfortunately, Budgets won't be available for now in API. We will inform you when it will be implemented.